Hydraulic fluids are low viscosity fluids used for the transmission of useful power by the flow of the fluid under pressure from a power source to a load. A liquid hydraulic fluid generally transmits power by virtue of its displacement under a state of stress. Hydraulic fluids generally also lower the coefficient of friction. To be effective, the compositions typically have sufficient antiwear, antiweld, and extreme pressure properties to minimize metal damage from metal-to-metal contact under high load conditions.
Hydraulic fluids are usable in blowout preventer (BOP) devices which are used to control well-head pressure of an oil well that is being drilled and/or in marine environments such as in off-shore oil drilling rigs. A “blowout” is defined herein as an uncontrolled flow of gas, oil, or other well fluids into the atmosphere or into an underground formation. A blowout (or gusher) can occur when formation pressure exceeds the pressure applied to it by the drilling or extraction apparatus. Thus, a “blowout preventer” is one of several valves installed at the wellhead to prevent the escape of pressure either in the annular space between the casing and drill pipe or in open hole (i.e., hole with no drill pipe) during drilling completion operations. The blowout preventer is a hydraulic device that forms a virtually instantaneously seal around the drill string to seal off well-head pressure when an area of high pressure such as a high pressure gas pocket has been contacted. BOP's on land rigs are typically located beneath the rig at the land's surface; on jackup or platform rigs, are located at the water's surface; and on floating offshore rigs, are located on the seafloor. A BOP control unit stores hydraulic fluid under pressure and provides a mechanism for opening and closing the BOP's quickly and reliably. The opening and closing forces in the unit are typically provided by compressed air and hydraulic pressure.
There are many reported problems associated with conventional hydraulic fluids used in BOP applications. For example, the handling of many conventional hydraulic fluids may be complicated by their combustibility, i.e., low flash points, and poor fire resistance. In addition, many conventional hydraulic fluids are toxic and accidental spillage, especially into the ocean, creates significant environmental problems.
Many conventional hydraulic fluids are not suitable for BOP applications due to their low tolerance to sea water contamination or to contamination by hydrocarbons, i.e., they tend to readily form emulsions with small amounts of hydrocarbons. Furthermore, in marine environments, problems arise due to the lack of biodegradability of the hydraulic fluid and to bacterial infestations arising in the hydraulic fluid, especially from anaerobic bacteria such as the sulfate reducing bacteria prevalent in sea water.
Other problems associated with the use of conventional hydraulic fluids under the extreme conditions encountered in BOP devices include: (1) some conventional hydraulic fluids may, cause corrosion with metals in contact with the fluid; (2) some conventional hydraulic fluids are reactive with paints or other metal coatings or tend to react with elastomeric substances or at least cause swelling of the elastomeric substance; (3) poor longterm stability, especially at elevated temperatures; (4) some hydraulic fluids require anti-oxidants to avoid the oxidation of contained components; (5) some hydraulic fluids are not readily concentrated for ease in shipping; and (6) many conventional hydraulic fluids have a non-neutral pH, thereby enhancing the opportunity for reaction with materials in contact with it. For all of these reasons, it has become advantageous to use aqueous hydraulic fluids in BOP applications and various aqueous formulations have been developed that are usable in such applications.
In addition, the demand for aqueous based hydraulic fluid compositions such as may be used in BOP devices continues to increase due to the environmental, economic and safety (e.g. high non-flammability) advantages of such fluids over conventional non-aqueous, oil-type hydraulic fluids.
The OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic, provides a list of substances used in preparations used and discharged offshore which are considered to Pose Little or No Risk to the Environment (PLONOR) which do not need to be heavily regulated. Thus, it would be desirable to have an aqueous hydraulic fluid composition that is usable in BOP applications and contains substantially only substances that are PLONOR approved.
An example of an aqueous hydraulic fluid composition that is usable in BOP devices is described in U.S. Patent Publication No. 2007/0078068 to Askew, the subject matter of which is herein incorporated by reference in its entirety. Askew describes an aqueous hydraulic fluid composition comprising at least one phospholipid lubricant which is preferably a plant-derived lecithin as the only lubricant in the composition and less than 20% by weight of a mineral oil, synthetic hydrocarbon oil or mixture thereof. Another example of an aqueous hydraulic fluid composition is described in U.S. Pat. No. 5,698,498 to Luciani et al., the subject matter of which is herein incorporated by reference in its entirety.
The inventor of the present invention has identified additional additives that can provide improved lubricity and improved stability of aqueous hydraulic fluid compositions that are usable under the extreme conditions encountered in BOP devices.
To that end, the inventor of the present invention has determined that the use of a stearate such as calcium stearate provides improved lubricity of the aqueous hydraulic fluid composition. The use of calcium stearate in the composition also provides significantly increased stability of the composition. Calcium stearate is also on the PLONOR list of acceptable substances.